1. Field of the Invention
The present invention is directed to a system and method for the forming of local features in, and/or accomplishing the localized joining of sheet materials of various composition, by the contacting of the materials with a high-velocity projectile. The system and method The area of the sheet material to be formed is placed over a forming die having a cavity of desired shape. A preferably deformable projectile is then propelled into the area of the sheet material to be formed, such that a portion of the material is driven into the forming die. The system and method of the present invention may be used to form particular features in the sheet material, to join two or more sheets of material, or to connect a sheet of material to a secondary component. When more than one material is used, the materials may be of like composition or, alternatively, the system and method of the present invention may be employed to join dissimilar materials.
2. Background
Many products are manufactured from metallic or other sheet materials, wherein the products require the forming of particular, localized features at certain locations thereon. Similarly, there are many products whose manufacture requires the attachment of one or more secondary components to a sheet material at one or several localized sites. In a typical attachment process, a secondary component may be locally joined to a sheet material by forcing a portion of the material through an opening in the component and into a subjacent cavity, whereby the shape of a cavity into which the material is forced thereafter causes the material to expand outwardly, mechanically connecting the sheet of material and the second component. Two or more sheet materials may also be locally joined by employing the system and method of the present invention. Manufacturers of aluminum cans, and automotive and aerospace products, for example, commonly employ systems and methods for effecting localized feature forming, the attachment of secondary components, and/or the localized joining of metallic materials. Such a system and method may be used, for example, to attach a pull tab to the top of a can for containing a beverage or a foodstuff.
There are known systems for providing localized feature forming and/or the localized joining of metallic materials. The most commonly employed system is likely that of the punch and die. In a punch and die system, one or more sheets of metallic material are placed between a cavity containing die and a corresponding punch. The punch and die are typically disposed on opposing portions of a forming machine, such as a hydraulic press or similar device. The forming machine causes the punch and die to come together, whereby the punch forces a portion of the metallic material into the die cavityxe2x80x94producing a formed feature in the material. Similarly, two or more sheet materials may be placed over a die having a properly shaped cavity, such that when the punch forces the materials into the cavity each of the materials is caused to bulge outwardly, thereby effectively affixing each material to the other by way of an interlocking shape. Such a process of mechanically interlocking the two or more materials is commonly referred to as spot clinching. It is also possible to attach a secondary component to a sheet material by using the punch to force a portion of the material through an aperture in the secondary component, and thereafter causing the material to expand outwardly beyond the circumference of the aperturexe2x80x94thereby effectively locking the seconadry component to the sheet material. While the punch and die method of feature forming and localized joining is likely the most common method in use, it is not without limitations and problems. This process is generally limited to high ductility materials, because the operation of the punch and die generates a high shear force and may also cause a significant thinning of the materials to which it is applied. Such a mechanical process also typically requires a large structure for supporting the materials to be formed or joined, as well as a large force generating device, such as the hydraulic press mentioned above, to drive the punch into the die. In mechanical joining processes, the materials are also limited to joining by interlocking of the shapes produced by the punch and die, as a metallurgical bond between the materials cannot be developed thereby.
Electromagnetic forming has been used to generate high-velocity movement of a sheet, which can then be used to impart a shape to both entire metal sheets, and to smaller, localized features within a metal sheet. While electromagnetic forming has proven effective for use in forming large features, it is typically less effective when utilized to form smaller, localized features. The forming of localized features often requires the application of very high and localized forces. In such cases, process efficiency suffers, and small robust actuators are quite difficult to fabricate. Consequently, because it is very difficult to focus sufficient electromagnetic energy on a small surface area, it is genarally not practical to use an electromagnetic forming process in this manner.
Localized high explosives have been used for some time to join primarily dissimilar metallic components. Typically, one component is situated at a slight distance from the other component, so that an explosive charge can be used to drive the components into contact with one another. The explosive charge causes the components to collide at a sufficient velocity and angle to form a metallurgical bond therebetween. Explosive welding is commonly used to create sealed joints, such as vacuum joints, between metals such as aluminum, copper and stainless steel. Other uses for explosive welding may include the placement of a cladding onto a steel substrate, and the joining of aluminum to low-expansion metals in the electronics industry. Explosive welding is not typically used to form localized features or to join thin metallic sheets.
Ultrasonic or friction welding has also been used to join metallic and non-metallic components. Such methods involve placing the components into contact and causing movement along the joint interface located therebetween. Commonly, a friction weld is generated by rotating one component against a fixed second component under pressure. In this manner, sufficient frictional heat can be produced between the components such that at least one of the components can become plastic at the joint interface. When the rotational motion is halted, the components become physically bonded together. Friction welding also generally requires that at least one of the components be circular at the joint interface. Friction welding cannot be used to form localized features, and also cannot be used to join sheets of metallic materials in localized areas.
Hyper-pressure water jet pulses have recently been proposed to accomplish the bonding of aluminum components. In this method, a hyper-pressure pulse is developed by directing a high-pressure water jet pulse through a tapered nozzle to further increase its acceleration and pressure. Aluminum components to be joined are placed on an assembly fixture where they can be contacted with the hyper pressure water jet pulse. The hyper pressure water jet pulse can be used to cause a mechanical interlocking of the components and, if the stagnation pressure of the pulse is sufficiently high, may cause a plastic deformation of the components. This technique requires an ultrahigh-pressure pumping system to generate hyper pressure water jet pulses. This technique also requires the use of a manipulator, such as a robotic arm, to place the water jet nozzle substantially against the materials to be formed or joined.
While it can be seen from the foregoing that there are various systems and methods for providing localized feature forming and joining of materials, some of which can be used to join dissimilar materials, there remains a need for a system and method that can produce localized features that cannot effectively be produced by these known methods. For example, it is desirable to satisfactorily produce localized features that currently typically result in a tearing or excessive thinning of the material or materials involved. There also remains a need for a system and method of efficiently producing a localized joining of multiple sheets of material, wherein more than a mechanical bond is created therebetween, and/or where the joining may be accomplished at arbitrary points over a large surface area. For example, to increase the strength of the joint created between the materials, it is desirable that a metallurgical bond be created, such as by causing the materials to become plastic in the joint area. Such a method may be used to join similar or dissimilar materials.
The present invention satisfies the aforementioned needs. The present invention provides a system and method of forming localized features in sheets of metallic material, as well as a system and method of joining multiple sheets at one or more locations by forming a metallurgical bond therebetween. The system and method of the present invention also allows for the attachment of secondary components to a sheet of material. The system and method of the present invention accomplishes these actions by contacting the sheet or sheets of material with a high-velocity projectile.
When used to form localized features, a sheet of material is preferably placed over a die containing a cavity, which cavity is of substantially the same shape as the desired localized feature to be formed. A projectile firing device is preferably located at some distance from the sheet of material and is substantially aligned with the die cavity. A preferably deformable projectile is then propelled from the projectile firing device into the sheet material, whereby the kinetic energy of the projectile forces a portion of the sheet of material into the die cavityxe2x80x94resulting in the formation of the localized feature.
When used to join two or more thin materials, the materials are similarly placed, preferably with substantially no gap therebetween, over a die containing a cavity. As in the forming method described above, the projectile firing device is used to fire a preferably deformable projectile into the materials where they overly the die cavity. Also as in the forming method, the materials are driven into the die cavity, wherein their shape is determined thereby. Using the system and method of the present invention, the materials may become joined by two mechanisms. First, the die cavity may be designed such that the materials will become mechanically interlocked with one another, such as is achieved in a traditional spot clinching process. Secondly, a metallurgical bond may be established between the materials as a result of the kinetic energy of the high-velocity projectile being transferred thereto. Thus, a stronger and more durable joint may be produced than may be accomplished by mechanical joining alone.
The projectile is preferably of a deformable material such as lead or plastic, but it is contemplated that other projectile materials may also be used, such as, for example, water in the form of liquid or ice. The projectile may be fired into the material(s) by any conventional means, such as, for example, by compressed air, explosive charge, electrical charge, or by any number of other means that are capable of accelerating the projectile to a sufficient velocity. The material(s) may be releasably secured in a position over the die cavity by clamping devices, by vacuum holding devices, or by means of a magnetic holding system.
Because the energy of the projectile can be effectively focused in a small region, the system and method of the present invention is especially useful for forming small and/or complex features, for achieving the localized joining of multiple sheets of material, in the attachment of secondary components to a sheet of material, or for joining a sheet material to a substantially more massive component. Also, it has been found through experimentation that the system and method of the present invention increases the forming limits of metallic sheet materials. More specifically, the system and method of the present invention appears to cause a through-thickness squeezing of the metallic material into the die cavity as opposed to causing a stretching of the material, thereby allowing the metallic sheet material to be thinned to a considerably greater degree without tearing than is typically possible by known forming systems and methods. Also, high-velocity deformation appears to actually inhibit the metal tearing process. Consequently, sharper, deeper, and more complex features may be formed without causing a tearing of the material, and lower ductility materials, which are typically stronger, may also be used. It has been found that the system and method of the present invention is also effective in minimizing or eliminating other problems associated with metal forming, such as, for example, wrinkling and distortion. When used to join multiple sheets of material, the system and method of the present invention has been found to produce joints of increased strength, as the kinetic energy imparted to the materials by the high-velocity projectile is sufficient to produce an inertial welding of the materials that results in a metallurgical bond therebetween.
There are also aspects of the system and method of the present invention other than those already described above. For example, the equipment required to produce high-velocity forming or joining using a projectile is inexpensive in comparison to the equipment required to achieve similar results by the known, aforementioned techniques. No hydraulic or other press device is required as in the traditional punch and die technique, therefore there is no need for a large framework or for a complex, two-part, forming/joining die. Additionally, in the case of the system and method of the present invention wherein the materials are magnetically held in position above the die cavity, features and joints may be produced at arbitrary locations about large sheets of material, without the large clamping and support frame generally required by known techniques. Thus, the system and method of the present invention offers numerous advantages over known systems for producing localized features in sheet materials, for accomplishing the localized joining of multiple sheets of material, and for attaching secondary components to a sheet of material.